1. Field of the Invention
The present invention relates to data storage devices, data recording methods, data playback methods, and program providing media. In particular, the present invention relates to a data storage device, a data recording method, a data playback method in which content stored in the storage device is protected under high security management, and a program providing medium used therewith.
2. Description of the Related Art
With the rapid spread of the Internet in recent years and the spread of compact mobile players and portable game machines, the distribution of various types of software data (hereinafter referred to as “content”), such as music data, game programs, and image data, via a network such as the Internet or by storage media, such as digital versatile disks (DVDs), compact disks (CDs), and memory cards, is rapidly increasing. The distributed content is received via the network and is stored in a play-only device or a storage medium of a game machine which belongs to a user, or a memory card containing the content is loaded into the game machine, whereby content-playback processing or the execution of a program can be performed.
Content storage devices include a flash memory, which is commonly used. The flash memory is a form of electrically rewritable, non-volatile memory called an “electrically erasable, programmable read-only memory (EEPROM)”. The degree of integration of conventional EEPROMs is limited because the use of two transistors for one bit results in a large occupied area per bit. Conversely, in the flash memory, by using an all-bit batch erasure, one bit is implemented by one transistor. It is expected that flash memories will replace recording media such as magnetic disks and optical disks.
A type of memory card is also known in which the flash memory can be loaded/unloaded into/from a data recording/playback device. By using this memory card, a digital audio recorder/player in which a memory card is used instead of a conventional disk medium such as CD or MiniDisk (registered trademark) (MD) can be provided.
When such a content storage device using the flash memory is used in a personal computer, a playback unit, or the like, a file management system called a “file allocation table (FAT)” is generally used as an access information table. In the FAT system, after defining necessary files, the parameters required for the files are sequentially set from the first file. As a result, the file size can be set to be variable, and one or more management units (e.g., sectors or clusters) can constitute one file. Details related matters to the management units are written in the FAT. In the FAT system, the file structure can be easily formed regardless of the physical properties of the recording medium. Accordingly, the FAT system can be employed not only in floppy disks and hard disks but also in magneto-optical disks. The FAT system is employed in the above memory card.
Various content, such as music data, image data, or programs, are accessed based on the FAT from, for example, the above flash memory in response to a user's instruction from an information device which is used as a playback unit, a game machine, or a personal computer, or to a user's instruction via an input device connected to the information device. The content is played back by the information device or on a display and a speaker which are connected thereto.
In general, the distribution rights, etc., of much software content, such as game programs, music data, and image data, are possessed by the creators and sellers of the content. Accordingly, in the distribution of the contents, security limitation of usage is commonly employed in which unauthorized duplication, etc., is prevented by permitting only a registered user to use the content.
One technique enabling limitation of use by the user is encryption processing on the content to be distributed. Specifically, various encrypted contents, such as encrypted audio data, image data, and game programs, are distributed via, for example the Internet, and only a person who is identified as a registered user is supplied with a means for decrypting the distributed content, that is, a decryption key.
The encrypted data can be processed to form usable decrypted data (plaintext) by performing decryption processing based on predetermined processes. This method of data encryption and decryption which uses an encryption key for information encryption processing and a decryption key for decryption processing has been conventionally known.
There is a case in which a content part is encrypted in order to protect copyright, etc. In this case, when a single encryption key is used to encrypt the entirety of the content part, a large number of codes are generated under the same encryption key. This results in a possibility that the codes may be easily attacked. Normally, it is preferable that, after dividing the content part as much as possible, the divided pieces of the content part be encrypted by using different encryption keys. The minimum unit of content encryption is a sector. In addition, a construction for securely storing a plurality of content keys is an issue.